1. Field of the Invention
The present invention relates to a minimally invasive method of determining a patient's left ventricular pressure waveform without placement of a catheter inside the left ventricle. More specifically, the present invention utilizes a computer to convert the patient's ejection phase waveform of the peripheral arterial pressure, and the filling phase waveform of the pulmonary capillary wedge pressure into portions of the left ventricular pressure waveform. These portions are then connected together to complete the left ventricular pressure waveform.
2. Prior Art
A plot or loop showing the left ventricular pressure to volume relationship has been believed to be one of the best parameters reflecting a patient's cardiac function. This left ventricular pressure to volume relationship loop consists of the left ventricular pressure waveform and the left ventricular volume waveform. Although a non-invasive left ventricular volume waveform can be obtained by radionuclide angiocardiography or echocardiography, a non-invasive left ventricular pressure to volume relationship loop is not available, due to the inability to measure the left ventricular pressure waveform by a non-invasive or minimally invasive method.
Dr. Cemil M. Puruts reported a method that required a radionuclide angiocardiography and an invasive method, placing a catheter into the left ventricle during cardiac surgery, to obtain a left ventricular pressure to volume relationship loop (The Journal of Nuclear Medicine 1988, 29:1492-1497).
In Daniel Bogen and Krishanu Gupta's method, an end-systolic pressure-volume relationship was measured by intraaortic balloon occlusion (U.S. Pat. No. 4,877,035, issued on Oct. 31, 1989). There are two differences between Bogen and Gupta's method and the present invention. First, Bogen and Gupta's method utilized a catheter in the arterial system, where the present invention utilizes a catheter in the venous system, thus making it less dangerous. Second, the minimally invasive method of the present invention can obtain an entire left ventricular pressure waveform, instead of just the end-systolic pressure point.
Joseph J. Panico found a non-invasive method to determine left ventricular end diastolic pressure by data processing analysis of the EKG waveform, first heart sound and carotid pulse waveform (U.S. Pat. No. 4,203,451, issued May 20, 1980). The method of the present invention uses the pulmonary capillary wedge pressure waveform to construct a full filling phase waveform of the left ventricular pressure, which is a closer physiologic property.
William T. Link's method obtained the systolic blood pressure by the diastolic blood pressure, arterial curve or amplitude curve and a different assumed systolic pressure (U.S. Pat. No. 4,564,020, issued on Jan. 14, 1986). Link's method did not involve the establishment of a left ventricular pressure waveform.
Thus, no minimally invasive method of determining the left ventricular pressure waveform is known at present.